Ventricles of the brain contain cerebrospinal fluid (CSF) which cushions the brain against shock. CFS is constantly being secreted and absorbed by the body usually in equilibrium. Cerebrospinal fluid is produced in the ventricles of the brain, where under normal conditions, it is circulated in the subarachnoid space and reabsorbed into the bloodstream, predominantly via the arachnoids villi attached to the superior sagittal sinus. However, if blockages in circulation of CSF, perhaps in the ventricles, CSF can't be reabsorbed by the body at the proper rate.
This can create a condition known as hydrocephalus which is a condition marked by an excessive accumulation of fluid violating the cerebral ventricles, then the brain and causing a separation of the cranial bones. Hydrocephalus is a condition characterized by abnormal flow, absorption or formation of cerebrospinal fluid within the ventricles of the brain which subsequently increases the volume and pressure of the intracranial cavity. If left untreated, the increased intracranial pressure can lead to neurological damage and may result in death.
Over the past 40 years, a common treatment for hydrocephalus patients has been the cerebrospinal fluid shunt. The standard shunt consists of the ventricular catheter, a valve and a distal catheter. The excess cerebrospinal fluid is typically drained from the ventricles to a suitable cavity, most often the peritoneum or the atrium. A catheter is tunneled into the brain through a burr hole in the skull. The catheter is placed into ventricles to shunt CSF to other areas of the body, principally the peritoneum, where it can be reabsorbed. The presence of the shunt relieves pressure from CSF on the brain.
A flow or pressure regulating valve is usually placed along the catheter path. Differences in pressure due, at least in part, to differences in vertical position between the inlet (ventricles) and the outlet (peritoneum) can create too much drainage with such a flow or pressure regulating valve.
An alternative, and newer, method to shunting CSF to the peritoneum is to shunt CSF from the ventricles to the sagittal sinus.
A conventional technique for placing a catheter in the ventricles in the brain is to first drill a burr hole in the skull. A scalpel can then be used to create a slit in the dura surrounding the brain to gain access. However, controlling the length of the slit in the dura is difficult and will vary from surgery to surgery.
An alternative method after first drilling a burr hole is to use cautery to heat/burn tissue of the dura to create and opening in the dura. Still, controlling the shape and diameter of the opening in the dura is difficult and, again, will vary from surgery to surgery.
The holes provided by the preceding techniques provide a pathway to the ventricles. A catheter is then intubated into the lateral ventricle which remains in place in the patient.
Both standard methods of entry allow for leakage of CSF around the outer surface or diameter of the catheter from the dura post-implant. Leakage of CSF through the dura can cause serious surgical complications including infection, severe headaches and disturbances of hearing or vision. It can also lead to changes in pressures of fluid in the ventricular/shunt system and result in complications and failures. It has been estimated that approximately forty percent (40%) of initial ventricular shunt installations require correction or revision.
The shunt implantation procedure is associated with the known incidents of complications that are recognizable and treatable. Of these, ventricular catheter obstruction is the most common reason for revision followed by infection. When shunting from the ventricles to the venous system, either via the right auricle or the dural sinuses, thrombo-embolic complications and the dissemination of infection through the bloodstream are additional risks.
Shunting can also be accomplished from the ventricles to the sagittal sinus, particularly the superior sagittal sinus. This procedure involves making a second entry into the cranium in order to install an outlet catheter into the sagittal sinus. Placing a distal catheter in the blood stream of the sagittal sinus creates the potential for blood clotting and resulting occlusion of the sinus passageway.